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Coupling and uncoupling of CYP2C9 and its variants in metabolism of the atypical kinetics substrate naproxen
Author(s) -
Wei Lian,
Locuson Charles W.,
Tracy Timothy S.
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.4.a263-a
Subject(s) - cyp2c9 , reductase , metabolite , chemistry , cytochrome p450 , metabolism , biochemistry , substrate (aquarium) , enzyme , biology , ecology
CYP2C9 is the primary human hepatic cytochrome P450 metabolizing S‐naproxen and this process exhibits atypical, biphasic kinetics. CYP2C9 polymorphisms [e.g., CYP2C9*2 (R144C) and CYP2C9*3 (I359L)] are associated with lower rates of metabolism and the R144C variant has been hypothesized to alter interactions of CYP2C9 with the redox partner P450 reductase. To assess the role of these polymorphisms on P450 cycle coupling and uncoupling, metabolite and hydrogen peroxide formation in addition to oxygen and NADPH consumption were monitored during co‐incubation of S‐naproxen and CYP2C9 and over a range of P450 reductase concentrations. Metabolite formation increased up to a reductase:P450 ratio of 4 and then decreased in all cases (CYP2C9.1>CYP2C9.2>CYP2C.3). Uncoupling (H 2 O 2 /O 2 ratio) was greatest for CYP2C9.3, whereas uncoupling was roughly equal for CYP2C9.1 and CYP2C9.2 up to a reductase:P450 ratio of 1. Increasing the reductase:P450 ratio above 1 resulted in a greater decrease in uncoupling of CYP2C9.2 than in wild type enzyme due to a greater reduction in H 2 O 2 formation. Coupling (metabolite/NADPH) was highest for CYP2C9.1, followed by CYP2C9.2 and CYP2C9.3. Furthermore, increasing reductase concentrations increased coupling in all cases but to varying degrees. In summary, differences in coupling and effects of reductase concentration were noted among the CYP2C9 variants, helping explain reduced substrate turnover by CYP2C9.2 and CYP2C9.3. Support: NIH # 063215 and 069753